Injection-molding machines generally comprise a device for moving one such plate toward and away from another plate and may include hydraulic or other power systems for moving this plate or both plates in a mold-closing or mold-opening operation. For example, the movable plate or plates may be mounted on pistons of hydraulic cylinders which move the plates carrying the mold halves toward one another in the mold-closing operation in which the mold halves are held forceably together against the injection pressure which develops within the mold cavity. Means is provided in at least one of the plates for injecting the settable material into the mold cavity therethrough and it is customary to provide these plates with means for attaching the respective mold halves thereto.
The mold itself may consist of two or more relatively movable parts which, when brought together, define the mold cavity into which the material can be injected.
In general, one of these parts, referred to for convenience as a mold half whether or not it consists of a complete half of the mold structure, is secured to one plate for movement therewith while the other mold half is secured to the other plate.
Since injection-molding machines are comparatively expensive and a long downtime may result in a substantial drop in the output of a plant, the time required for changeover of a mold, e.g. for production of a different item or simply for replacement of a worn or damaged mold, is a problem. Efforts have been made to reduce the downtime by providing quick-change mold systems, i.e. mold assemblies which can be introduced and removed relatively rapidly and which minimize hand efforts which are required to secure the mold parts to the respective plates.
One such quick-change system is available from the Austrian firm Ludwig Engel KG Machinenfabrik, A-4311 Schwertberg, Austria and is described in a prospectus identified as Engel Information A-67-TV-9/81. In this arrangement, a mold provided with a clamping device to hold the parts together or a device for aligning them and retaining them in alignment in a closed state, can be bodily introduced between the plates of the injection-molding machine. The two mold halves are thus in a comparatively short time affixed to the injection-molding machine plates or released therefrom so that downtime for mold replacement is minimized.
It is, however, a residual disadvantage of this system that, for security each mold half much be secured at its rear side and via traction bolts projecting therefrom, aligned with and secured to or centered on the mold-carrying plates of the injection molding machine.
Thus, notwithstanding the fact that the earlier system permitted fairly rapid mold replacement, problems of alignment and positioning continued to confront the art.
Another disadvantage of such earlier systems, resulting from the way in which the mold halves are mounted on the plate, is that for mold replacement, i.e. removal and attachment, it is necessary to shift each mold half and the respective mold-carrying plate in the direction of the opening and closing movement, notwithstanding the fact that the introduction of the mold into position and its removal are best effected transversely to this direction.
This complicates the manipulative steps, and because outwardly projecting bolts, alignment pins and like formations are provided on the backs of the mold halves, the molds cannot readily be stored or even handled with ease.
Still another disadvantage of the earlier systems is that the mold replacement cannot be conveniently monitored, i.e. it is difficult to see how the parts are being aligned or relatively positioned during the mold replacement operations. It is therefore necessary to provide indicators for locking devices such as the locking keys which can display the position of the parts which must secure the mold halves to the mold plates. In general, therefore, while the earlier system has advanced the art by simplifying mold replacement to a certain extent, it has not fully solved the problems and is itself accompanied by problems which make use of the system difficult.